The present invention relates to a device for controlling a sewing machine having a feed reversing mechanism.
A conventional sewing machine control device of this type is shown in FIG. 1. In FIG. 1, reference numeral 1 designates a sewing machine head; 2, a feed reversing mechanism; 3, a position detector for detecting the position of the needle of the sewing machine head 1, the detecting means 3 being mounted on the rotary shaft 1a of the sewing machine head 1; and 4, and electric motor for driving the sewing machine head 1. The torque of the output shaft 4a of the motor is transmitted through a pulley 13 and a belt 14 laid therearound to a pulley 15 mounted on the rotary shaft 1a.
Further in FIG. 1, reference numeral 5 designates a pedal; 6, a reverse stitching speed setting mechanism; 7, a stitch setting mechanism; 8, a motor control section for applying an operating signal to the motor 4 according to a signal outputted by the pedal 5 and data provided by the mechanisms 6 and 7; and 9, a feed reversing mechanism control section for driving the feed reversing mechanism 2 according to data provided by the position detector 3 and the stitch setting machanism 7.
The operation of the sewing machine control device thus contructed will be described.
The sewing machine head 1 is coupled to the motor 4. When the pedal 5 is depressed, the motor control section 8 applies the operating signal to the motor 4, causing the later to rotate, and thereby starting the sewing operation. In a reverse stitching operation, the number of stitches for reverse stitching is set by the stitch setting mechanism 7. When the pedal 5 is operated, the motor control section 8 supplies the operating signal to the motor 4 according to a speed set by the reverse stitching speed setting mechanism. The feed reversing mechanism control section 9 compares the number of stitches sewed, which is the output signal of the position detector 3, with the number of stitches instructed by the stitch setting mechanism 7, to thereby drive the feed reversing mechanism 2 for a perdetermined time period corresponding to the instructed number of stitches.
In the conventional sewing machine control device constructed as described above, the time period during which the feed reversing mechanism is driven for an instructed number of stitches is fixed. Therefore, the control device is disadvantageous in that, if the speed of the sewing machine is increased, because the feed reversing mechanism will start operating later than the time instant corresponding to the instructed number of stitches, the number of stitches actually sewed will be different from the instructed number of stitches.